This invention is concerned with television systems, and is particularly directed to projection television systems in which discrete images are projected on a viewing screen to provide a composite color picture.
In FIG. 1 there is depicted schematically the essentials of such a projection television system. The system 70 has a viewing screen 72 for displaying a light image cast thereon. Screen 72 is remotely located from a plurality of light projection means 74, 75 and 76. Two of the light projection means, designated as being projection means 75 and 76, have projection optical axes 78 and 79, respectively, lying at a non-zero, acute-angle A with respect to the viewing screen axis 80. These are termed "off-axis", or "displaced axis" tubes.
With reference also to FIG. 2 wherein off-axis projection means 76 is depicted in greater detail, projection means 76 is indicated as including a cathode ray tube means 82 having a cathodoluminescent screen 84 on the inside surface of the face panel 86 whose axis is substantially parallel to the projection optical axis 79. The seal land 85 indicates the junction of the seal edge of face panel 86 and the seal edge of funnel 87 of cathode ray tube 82; the significance of the seal edges and the seal land 85 and their orientation is described infra. The screen is made cathodoluminescent by a deposit of a monochrome phosphor which may comprise, for example, one of a number of phosphors emitting red, green or blue light upon excitation by an electron beam. The electron beam generating means 88, which is typically an electron gun, is disposed on the electron-optical axis 90 of cathode ray tube 82. Electron beam generating means 88 is indicated as emitting a scanning electron beam 92 which forms an electron image on the cathodoluminescent screen 84 in response to television signal information. The electron image is converted to a visible image by cathodoluminescent screen 84 as screen 84 is excited by beam 92.
Lens means 94 on projection optical axis 79 provides for projecting on viewing screen 72 the light image of the electron-formed visible image on cathodoluminescent screen 84. The light image inherently has a non-linear magnification distortion attributable to the location of projection means 76 off the viewing screen axis 80.
Two types of optical distortion are inherent in the system which can degrade through misconvergence the composite projected image to the point of unacceptability. The two types are trapezoidal distortion and horizontal non-linearity distortion, and are best described by the single term "non-linear magnification distortion." The non-linear magnification distortion exhibited by the light images projected on viewing screen 72 by light projection means 75 and 76 is shown in FIG. 1 as comprising, respectively, trapezoidally distorted images 96 and 98. An undistorted image 102 is represented by the solid lines. Horizontal non-linearity distortion is also present although not shown. It is manifested as a progressive stretching of the projected image from left to right as projected by projected means 76. Conversely, horizontal non-linear distortion of the image projected by projection means 75 is manifested by a progressive stretching of the image from right to left.
With reference again to FIG. 2, the projection television system according to the invention described and fully claimed in referent copending application Ser. No. 110,413, incorporated herein by reference, is characterized by the electron-optical axis 90 of cathode ray tube means 82 defining a non-zero, acute angle B with respect to the axis of cathodoluminescent screen 84. The value of angle B and the orientation of the electron-optical axis is selected to cause the electron-formed visible image to have an orientation and non-linear magnification distortion effective to substantially compensate for the off-axis-induced non-linear distortion of the projected light image.
The remedial effect is depicted in FIG. 3, which is view looking over the screen 72 and toward the projection television system 70. The electron-formed visible images 104A and 104A' have an orientation and non-linear magnification distortion effective to substantially compensate for the off-axis-induced non-linear magnification distortion of the projected light image. Images 104A and 104A' are shown as being reversed in orientation by transmission through lens means 94 and 94'. The shapes of the images in space as projected on viewing screen 72 are indicated respectively by light images 104B and 104B'. It will be seen that images 104A and 104A' upon projection substantially compensate for the off-axis-induced non-linear magnification distortion, as indicated by the composite image 105 cast on viewing screen 72, depicted as being substantially free of trapezoidal distortion, and which is also free of horizontal non-linearity distortion.
Off-axis light projection means 75 is substantially identical to light projection means 76, and can be considered to be its mirror image, with the orientation of components substantially reversed.
Light projection means 74 is shown as being on-axis; that is, the electron optical axis 106 of the cathode ray tube 108 is coincident with its projection optical axis and the axis 80 of viewing screen 72. Also, the electron-formed visible image 110A formed on its cathodoluminescent screen 112 is reactilinear. As a result, the light 110B projected by lens means 114 is also rectilinear, and the light image cast on screen 72 is in turn rectilinear and in coincidence with the images projected by light means 75 and 76, forming composite image 105.
Bennett et al in U.S. Pat. No. 3,369,881 discloses a method comprising the preparation of the funnel members and face panel members of cathode ray tubes for optimum alignment and sealing of such parts in the fabrication of tube envelopes. The method comprises the steps of forming complemental viewing panel portions and funnel portions for rectangular cathode ray tube envelopes. Each of the parts is formed with a plurality of external complemental reference protuberances. The reference protuberances on the funnel are used in the alignment of the neck and funnel prior to their conjoinment. Reference summits are ground on the protuberances on each funnel-neck part in accordance with a rotational and lateral alignment of the funnel, and in accordance with an axial alignment of the neck. Each pair consisting of a funnel and a face panel, may be optimally referenced to each other before sealing together by means of the reference summits, using a suitable fixture.
Fyler in U.S. Pat. No. 2,961,560 discloses a color television picture tube which includes structural assemblies for retaining the aperture mask in a unique position relative to the phosphor dot screen. The major reference points for location of the mask are provided on or adjacent to the viewing end of the bulb. In one embodiment of the invention, cast projections are molded as part of the inner surface and are spaced about the periphery of the viewing end of the bulb. The aperture mask is provided with fittings which cooperate with the locating members. To maintain firm contact of the mask fittings for the locating members springs are provided.
Faceplate-funnel referencing means are disclosed in U.S. Pat. No. 4,028,580 to Dougherty. A color cathode ray tube is depicted including a shadow mask and improved suspension devices for suspending the mask adjacent the faceplate of the tube. The disclosure stresses channel-shaped studs comprising part of the suspension devices. Each of the studs has a first portion adapted to be imbedded in the faceplate and a second portion having provision for coupling the stud to the shadow mask. The studs engage reference surfaces on the inside of the funnel when the faceplate and funnel are mated and thereby served to reference to faceplate to the funnel.